Freeform surfaces have advantages on balancing asymmetric aberration of the unobscured push-broom imager. However, since the conventional paraxial aberration theory is no longer appropriate for the freeform system design, designers are lack of insights on the imaging quality from the freeform aberration distribution. In order to design the freeform optical system efficiently, the contribution and nodal behavior of coma and astigmatism introduced by Standard Zernike polynomial surface are discussed in detail. An unobscured three-mirror optical system with 850 mm effective focal length, 20°× 2° field of view (FOV) is designed. The coma and astigmatism nodal positions are moved into the real-FOV by selecting and optimizing the Zernike terms pointedly, which has balanced the off-axis asymmetric aberration. The results show that the modulation transfer function (MTF) is close to diffraction limit, and the distortion throughout full-FOV is less than 0.25%. At last, a computer-generated hologram (CGH) for freeform surface testing is designed. The CGH design error RMS is lower than λ/1000 at 632.8 nm, which meets the requirements for measurement.

Date Published: 24 October 2016
PDF: 6 pages
Proc. SPIE 9682, 8th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Large Mirrors and Telescopes, 96820F (24 October 2016); doi: 10.1117/12.2240382

Published in SPIE Proceedings Vol. 9682:
8th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Large Mirrors and Telescopes
Myung K. Cho; Bin Fan, Editor(s)